Synthesis of 2-alkynyl-, 4-alkynyl-, and 2,7-dialkynyl-1,8- bis(dimethylamino)naphthalenes and the unexpected influence of ortho -alkynyl groups on their basicity

Article abstract of DOI:10.1055/s-0033-1339339

Novel 2-alkynyl-, 4-alkynyl-, and 2,7-dialkynyl derivatives of 1,8-bis(dimethylamino)naphthalene ('proton sponge') have been synthesized and their basicity values have been measured by competitive NMR studies in DMSO. These indicate that, while the para-alkynyl groups decrease the basicity of the parent proton sponge approximately by one order of magnitude in accordance with their electron-accepting nature, the influence of ortho-alkynyl functionalities is unexpectedly base-enhancing. The latter phenomenon has been ascribed to the appearance of a buttressing effect, but some other factors can be also at work. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0033-1339339

CLUSTER
▌2515
cluster
Synthesis of 2-Alkynyl-, 4-Alkynyl-, and 2,7-Dialkynyl-1,8-bis(dimethyl-
amino)naphthalenes and the Unexpected Influence of ortho-Alkynyl Groups
on Their Basicity
Alkynyl-Substituted 1,8-Bis(dimethylamino)naphthalenes
Ekaterina A. Filatova, Alexander F. Pozharskii,* Anna V. Gulevskaya, Nikolay V. Vistorobskii, Valery A. Ozeryanskii
Department of Organic Chemistry, Southern Federal University, Zorge 7, 344090 Rostov-on-Don, Russian Federation
Fax +7(863)2975146; E-mail: apozharskii@sfedu.ru
Received: 31.05.2013; Accepted after revision: 11.06.2013
magnitude more basic than the parent sponge 1, and naph-
Abstract: Novel 2-alkynyl-, 4-alkynyl-, and 2,7-dialkynyl deriva-
thalene-2,7-diolate 4 so strongly holds a proton chelated
tives of 1,8-bis(dimethylamino)naphthalene (‘proton sponge’) have
between the nitrogen atoms that it cannot be removed
been synthesized and their basicity values have been measured by
competitive NMR studies in DMSO. These indicate that, while the
even by metal hydrides in DMSO.7 The basicity of 4 has
para-alkynyl groups decrease the basicity of the parent proton been estimated to be in excess of 25 pKa units and, cur-
sponge approximately by one order of magnitude in accordance
with their electron-accepting nature, the influence of ortho-alkynyl
functionalities is unexpectedly base-enhancing. The latter phenom-
rently, it seems to be the most basic arylamine system.
However, several years ago we demonstrated that the high
basicity of 3, 4, and related compounds resulted not so
much from the ‘buttressing effect’ as from the electron-
donor nature of the methoxy and phenolate functional-
ities.7,8 The most conclusive evidence in favor of this view
is the relatively low basicity of 2,7-bis(trimethylsilyl) de-
rivative 5, which tallies with the weak electron-acceptor
property of the TMS group but not with its steric bulk.8,9
enon has been ascribed to the appearance of a buttressing effect, but
some other factors can be also at work.
Key words: amines, proton sponge, cross-coupling, alkynes,
buttressing effect, basicity
It is commonly accepted1 that the exceedingly high basic-
ity (pKa = 12.1 in water2 and 7.5 in DMSO3) of 1,8-bis(di-
methylamino)naphthalene (1, ‘proton sponge’) is mainly
caused by two factors: destabilization of free base 1 by
steric and electrostatic repulsion of the peri-NMe2 groups
and strong intramolecular hydrogen bonding in the pro-
tonated form 2 (Scheme 1).
Me2N
NMe2
Me2N
NMe2
–O
O–
MeO
OMe
3
4
pKa > 25
pKa = 16.1 (H2O)
pKa = 11.5 (DMSO)
B
Me2N
NMe2
Me3Si
SiMe3
Me
Me
Me
Me
H
N
N
N
+
N
Me
Me
Me
Me
BH+
5
pKa = 7.0 (DMSO)
– BH+
1
2
pKa = 12.1 (H2O)
pKa = 7.5 (DMSO)
Figure 1 Substituted proton sponges 3–5 showing variations in ba-
sicity
Scheme 1 Protonation–deprotonation of proton sponge 1
Starting from this precedent, the main goal of the work re-
ported herein was the preparation of novel 2-alkynyl (6),
2,7-dialkynyl (7), and 4-alkynyl (8) derivatives of 1,8-
bis(dimethylamino)naphthalene and a comparative study
of their basicity (Figure 2).
Alder’s discovery4 of proton sponges spurred interest in
the area of neutral organic superbases, in particular, pro-
moting a quest to create compounds with the highest ba-
sicity.5 One of the early approaches to this goal consisted
in placing the bulky substituents into positions ortho to
the NMe2 groups.6 It was argued that such substituents
would bring the peri-nitrogen atoms into closer proximity
(‘buttressing effect’) making the resulting base even more
destabilized and therefore stronger. Indeed, in several cas-
es this approach turned out to be fruitful. For example,
2,7-dimethoxy derivative 3 (Figure 1) is four orders of
We considered that the influence on basicity of ortho-
alkynyl groups, with the cylindrical symmetry of their tri-
ple bonds, weak electron-accepting strength (p = 0.23 and
0.16 for C≡CH and C≡CPh, respectively)10 and dimin-
ished steric bulk could be intriguing, if difficult to predict.
The desired acetylenes 6–8 were obtained from the corre-
sponding iodides 9–118,11 and 1-alkynes by Sonogashira
coupling12 using Pd2(dba)3, CuI, Ph3P, K2CO3, and DMF
or Pd2(dba)3, CuI, Ph3P, and Et3N catalytic systems
(Scheme 2).13 Unfortunately, proton sponge bromides,
SYNLETT 2013, 24, 2515–2518
Advanced online publication: 17.07.2013
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0033-1339339; Art ID: ST-D0503-L
© Georg Thieme Verlag Stuttgart · New York

2516
E. A. Filatova et al.
CLUSTER
NMe2
NMe2
R
Me2N
NMe2
R
R
Me2N
NMe2
R
Me2N
Me2N
I
R
cat., Ar
50–60 °C, 8 h
6a (75%)
9
6
7
6b (61%)
6c (83%)
6d (85%)
Me2N
NMe2
i
NMe2
R
NMe2
R
Me2N
Me2N
I
I
R
cat., Ar
60 °C, 10 h
(for 7c: 70–75 °C, 2 h)
7a (60%)
10
R
7b (63%)
7c (34%)
7d (87%)
8
i
Figure 2 Structural motifs of new acetylenic compounds 6–8
NMe2
Me2N
NMe2
Me2N
which are generally more accessible,11,14 were non-reac-
tive. Even using iodides 9–11 as starting materials, the re-
actions required warming to 50–60 °C and reaction times
of 8–10 hours in order to furnish alkynes 6–8 in moderate
to good yields. Trimethylsilylacetylenes 6c and 7c were
then desilylated with KF in aqueous methanol producing
ethynyl derivatives 6d and 7d, respectively. Interestingly,
coupling 2-iodo-1,8-bis(dimethylamino)naphthalene (9)
with phenylacetylene took place without need for added
K2CO3 giving phenylethynyl derivative 6a in 30% yield.
Probably, compound 9 serves as the base. This shows that
the high basicity of proton sponges can, in principle, be
used for self-catalysis in cross-coupling reactions.
Ph
cat., Ar
60 °C, 8 h
I
11
R
8a (64%)
8b (50%)
8c (27%)
8d (65%)
ii
6–8: R = Ph (a), 4-Tol (b), SiMe3 (c), H (d)
Scheme 2 Synthesis of compounds 6–8. Reagents and conditions: i)
KF, H2O, MeOH, r.t., 12 h; (ii) KOH, H2O, MeOH, r.t., 1 h. Catalyst
for R = Ph, 4-Tol: Pd2(dba)3, CuI, Ph3P, K2CO3, DMF; catalyst for R
= TMS: Pd(dba)3, CuI, Ph3P, Et3N.
The pKa values of acetylenes 6–8 were determined in
DMSO-d6 with the help of 1H NMR analysis by the com-
petitive transprotonation between a base and a cation of
two compounds comparable in their pKa values (usually
an equimolar mixture of 1 and the perchlorate of the cor-
responding monoprotonated acetylene).8,15 The data ob-
tained are presented in Table 1. As expected, 4-ethynyl
derivatives 8a,b,d are 1–1.5 pKa units less basic than 1. In
contrast, 2-ethynyl-, and especially 2,7-diethynyl deriva-
tives, are notably more basic than the parent proton
sponge. With a high degree of probability, this can be
attributed to the ‘buttressing effect’ caused by the ortho-
alkynyl groups. As we have previously reported on the basis
of X-ray single-crystal measurements performed for com-
pound 7b and its perchlorate, the N···N distance in the
former (2.76 Å) is somewhat shorter than that in 1 (2.80
Å).16 This should lead to the extra destabilization of mol-
ecules 7 thus increasing their basicity in spite of the elec-
tron-accepting character of the ethynyl groups.
Table 1 Basicity Constants (pKa) of Alkynyl Derivatives of 1,8-
Bis(dimethylamino)naphthalenea
Compd
R
pKa
1
–
7.5
7.6
7.6
7.5
7.9
8.3
7.8
6.5
6.6
5.9
6a
6b
6d
7a
7b
7d
8a
8b
8d
Ph
4-Tol
H
Ph
4-Tol
H
Ph
4-Tol
H
In summary, 2-alkynyl-, 4-alkynyl-, and 2,7-dialkynyl de-
rivatives of the proton sponge have been synthesized for
the first time. It has been shown that 4-alkynyl groups ex-
hibit their usual inherent electron-withdrawing effect,
lowering the proton sponge basicity on one pKa unit and
more. At the same time, the ortho-alkynyl substituents,
contrary to their electronic nature, enhance the basicity by
0.1–0.8 pKa units. This can be attributed to the electro-
static repulsion of the free nitrogen electron pairs and the
π-electrons of the triple bonds (‘buttressing effect’).
a Conditions: DMSO-d6, 25 °C.
Acknowledgment
This work was supported by the Russian Foundation for Basic Re-
search (projects 11-03-00073 and 11-03-00079).
Synlett 2013, 24, 2515–2518
© Georg Thieme Verlag Stuttgart · New York

CLUSTER
Alkynyl-Substituted 1,8-Bis(dimethylamino)naphthalenes
2517
1,8-Bis(dimethylamino)-2-(trimethylsilylethynyl)-
naphthalene (6c)
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnoIufproig
m
iotSrat
ungIifoop
r
t
Dark yellow oil. 1H NMR (250 MHz, CDCl3): δ = 0.25 (9 H,
s, SiMe3), 2.78 (6 H, s, NMe2), 3.09 (6 H, s, NMe2), 6.91 (1
H, m, Harom), 7.24–7.35 (4 H, m, Harom). 13C NMR (62.9
MHz, CDCl3): δ = 0.5, 45.0, 45.1, 82.4, 99.1, 107.3, 114.0,
122.0, 122.7, 126.8, 131.3, 138.4, 138.5, 152.1, 153.1. IR:
2140 (C≡C), 1553 (ring) cm–1. MS: m/z (%) = 310 (51) [M]+,
295 (29), 279 (24), 264 (22), 238 (30), 221 (17), 206 (51),
192 (30), 73 (100). Anal. Calcd for C19H26N2Si: C, 73.49; H,
8.44; N, 9.02. Found: C, 73.58; H, 8.29; N, 9.23.
2-Ethynyl-1,8-bis(dimethylamino)naphthalene (6d)
Dark yellow oil. 1H NMR (250 MHz, CDCl3): δ = 2.86 (6 H,
s, NMe2), 3.20 (6 H, s, NMe2), 3.45 (1 H, s, ≡CH), 7.04 (1 H,
m, Harom), 7.31–7.45 (4 H, m, Harom). 13C NMR (62.9 MHz,
CDCl3): δ = 45.0, 45.2, 82.4, 85.6, 113.6, 114.2, 122.1,
122.9, 123.0, 126.9, 131.4, 138.5, 152.1, 153.3. IR: 3303
(≡CH), 2093 (C≡C), 1600, 1553 (ring) cm–1. MS: m/z (%) =
238 (95) [M]+, 223 (18), 206 (70), 192 (83), 178 (21), 165
(18), 152 (31), 139 (15), 111 (21), 103 (23), 89 (25), 76 (33),
63 (34), 58 (69), 32 (100). Anal. Calcd for C16H18N2: C,
80.63; H, 7.61; N, 11.75. Found: C, 80.50; H, 7.79; N, 11.81.
1,8-Bis(dimethylamino)-2,7-bis(phenylethynyl)-
naphthalene (7a)
References and Notes
(1) (a) Pozharskii, A. F.; Ozeryanskii, V. A. In The Chemistry of
Anilines; Rappoport, Z., Ed.; Part 2; John Wiley and Sons:
Chichester, 2007, Chapt. 17,: 931–1026. (b) Alder, R. W.
Chem. Rev. 1989, 89, 1215. (c) Howard, S. T. J. Am. Chem.
Soc. 2000, 122, 8238.
(2) Hibbert, F. J. Chem. Soc., Perkin Trans. 2 1974, 1862.
(3) Benoit, R. L.; Lefebvre, D.; Frechette, M. Can. J. Chem.
1987, 65, 996.
(4) Alder, R. W.; Bowman, P. S.; Steele, W. R. S.; Winterman,
D. R. J. Chem. Soc., Chem. Commun. 1968, 723.
(5) (a) Superbases for Organic Synthesis: Guanidines,
Amidines, Phosphazenes and Related Organocatalysts;
Ishikawa, T., Ed.; John Wiley and Sons: Chichester, 2009,
326. (b) Pozharskii, A. F.; Ozeryanskii, V. A.; Filatova, E.
A. Chem. Heterocycl. Compd. 2012, 48, 200.
(6) (a) Alder, R. W.; Goode, N. C.; Miller, N.; Hibbert, F.;
Hunte, K. P. P.; Robbins, H. J. J. Chem. Soc., Chem.
Commun. 1978, 89. (b) Hibbert, F.; Simpson, G. R. J. Chem.
Soc., Perkin Trans. 2 1987, 243.
Yellow solid, mp 156–157 °C (from EtOH or n-octane). 1H
NMR (250 MHz, CDCl3): δ = 3.20 (12 H, s, 2 NMe2), 7.33–
7.47 (10 H, m, Harom), 7.55–7.62 (4 H, m, Harom). 13C NMR
(62.9 MHz, CDCl3): δ = 45.0, 91.0, 94.5, 117.0, 123.5,
124.4, 126.3, 128.0, 128.5, 131.0, 131.5, 138.0, 153.0. IR:
2211 (C≡C) cm–1. MS: m/z (%) = 414 (94) [M]+, 399 (39),
382 (100), 368 (31), 307 (25), 91 (29), 58 (23). Anal. Calcd
for C30H26N2: C, 86.92; H, 6.32; N, 6.76. Found: C, 87.09;
H, 6.17; N, 6.84.
(7) Ozeryanskii, V. A.; Milov, A. A.; Minkin, V. I.; Pozharskii,
A. F. Angew. Chem. Int. Ed. 2006, 45, 1453.
(8) Pozharskii, A. F.; Ryabtsova, O. V.; Ozeryanskii, V. A.;
Degtyarev, A. V.; Kazheva, O. N.; Alexandrov, G. G.;
Dyachenko, O. A. J. Org. Chem. 2003, 68, 10109.
(9) Degtyarev, A. V.; Ryabtsova, O. V.; Pozharskii, A. F.;
Ozeryanskii, V. A.; Starikova, Z. A.; Sobczyk, L.;
Filarowski, A. Tetrahedron 2008, 64, 6209.
(10) Exner, O. In Correlation Analysis in Chemistry. Recent
Advances; Chapman, N. B.; Shorter, J., Eds.; Plenum: New
York/London, 1978, 456–457.
(11) Ryabtsova, O. V.; Pozharskii, A. F.; Ozeryanskii, V. A.;
Vistorobskii, N. V. Russ. Chem. Bull. 2001, 50, 854.
(12) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett.
1975, 16, 4467.
1,8-Bis(dimethylamino)-2,7-bis(p-tolylethynyl)-
naphthalene (7b)
Yellow-orange solid, mp 155–156 °C (from i-PrOH). 1H
NMR (250 MHz, CDCl3): δ = 2.36 (6 H, s, 2 CMe), 3.15 (12
H, s, 2 NMe2), 7.17 (4 H, d, J = 7.9 Hz, 4-Tol), 7.32 (2 H, d,
J = 8.5 Hz, Harom), 7.40 (2 H, d, J = 8.5 Hz, Harom), 7.43 (4 H,
d, J = 7.9 Hz, 4-Tol). 13C NMR (62.9 MHz, CDCl3): δ = 22.0,
45.0, 90.5, 95.0, 117.5, 121.5, 124.0, 126.8, 129.5, 131.5,
131.8, 138.0, 138.5, 153.0. IR: 2210 (C≡C) cm–1. MS: m/z
(%) = 442 (100) [M]+, 427 (40), 410 (89), 396 (33), 320 (22),
221 (20), 205 (21), 191 (17), 175 (26). Anal. Calcd for
C32H30N2: C, 86.84; H, 6.83; N, 6.33. Found: C, 87.00; H,
6.95; N, 6.23.
(13) 1,8-Bis(dimethylamino)-2-(phenylethynyl)naphthalene
(6a)
Yellow solid; mp 98–100 °C (from EtOH). 1H NMR (250
MHz, CDCl3): δ = 2.78 (6 H, s, NMe2), 3.16 (6 H, s, NMe2),
6.95 (1 H, dd, J = 6.0, 2.8 Hz, Harom), 7.28–7.40 (7 H, m,
H
arom), 7.54 (2 H, dd, J = 7.7, 1.8 Hz, Harom). 13C NMR (62.9
MHz, CDCl3): δ = 45.0, 45.2, 91.5, 94.5, 114.2, 114.7,
122.0, 123.0, 124.8, 126.8, 128.0, 128.8, 131.0, 131.3,
138.2, 152.0, 152.5. MS: m/z (%) = 314 (90) [M]+, 299 (24),
282 (72), 268 (77), 254 (29), 226 (35), 207 (37), 196 (27),
167 (26), 157 (25), 149 (29), 141 (29), 133 (25), 127 (53),
113 (38), 103 (26), 91 (70), 77 (68), 58 (72), 51 (35). 44
(100). Anal. Calcd for C22H22N2: C, 84.04; H, 7.05; N, 8.91.
Found: C, 83.87; H, 7.23; N, 9.03.
1,8-Bis(dimethylamino)-2,7-bis(trimethylsilylethynyl)-
naphthalene (7c)
Dark yellow oil. 1H NMR (250 MHz, CDCl3): δ = 0.24 (18
H, s, 2 SiMe3), 3.06 (12 H, s, 2 NMe2), 7.20 (2 H, d, J = 8.5
Hz, Harom), 7.27 (2 H, d, J = 8.5 Hz, Harom). IR: 2133 (C≡C),
1525 (ring) cm–1. Anal. Calcd for C24H34N2Si2: C, 70.88; H,
8.43; N, 6.89. Found: C, 71.04; H, 8.54; N, 6.71.
2,7-Diethynyl-1,8-bis(dimethylamino)naphthalene (7d)
Yellow oil. 1H NMR (250 MHz, CDCl3): δ = 3.09 (12 H, s,
2 NMe2), 3.37 (1 H, s, ≡CH), 7.27 (2 H, d, J = 8.9 Hz, Harom),
7.33 (2 H, d, J = 8.95 Hz, Harom). 13C NMR (62.9 MHz,
CDCl3): δ = 45.2, 83.0, 85.0, 115.8, 123.6, 126.1, 132.5,
138.4, 154.0. IR: 3300 (≡CH), 2090 (C≡C), 1540 (ring) cm–1.
MS: m/z (%) = 262 (100) [M]+, 230 (59), 216 (41). Anal.
Calcd for C18H18N2: C, 82.41; H, 6.92; N, 10.68. Found: C,
82.62; H, 6.71; N, 10.78.
1,8-Bis(dimethylamino)-2-(p-tolylethynyl)naphthalene
(6b)
Yellow solid; mp 89–92 °C (from EtOH). 1H NMR (250
MHz, CDCl3): δ = 2.37 (3 H, s, CMe), 2.79 (6 H, s, NMe2),
3.18 (6 H, s, NMe2), 6.95 (1 H, dd, J = 6.3, 2.4 Hz, Harom),
7.16 (2 H, d, J = 8.1 Hz, p-Tol), 7.24–7.40 (4 H, m, Harom),
7.43 (2 H, d, J = 8.1 Hz, 4-Tol). 13C NMR (62.9 MHz,
CDCl3): δ = 22.0, 45.0, 45.2, 91.0, 94.8, 114.0, 115.0, 119.2,
121.8, 122.1, 123.0, 126.8, 129.8, 131.0, 131.2, 138.2,
138.3, 152.0, 152.1. MS: m/z (%) = 328 (100) [M]+, 313
(25), 296 (74), 282 (66), 268 (17), 206 (18), 196 (20), 164
(21), 149 (22), 141 (17), 134 (18), 127 (20). Anal. Calcd for
C23H24N2: C, 84.11; H, 7.37; N, 8.53. Found: C, 84.24; H,
7.26; N, 8.37.
1,8-Bis(dimethylamino)-4-(phenylethynyl)naphthalene
(8a)
Yellow solid; mp 147–149 °C (from EtOH). 1H NMR (250
MHz, CDCl3): δ = 2.80 (6 H, s, NMe2), 2.85 (6 H, s, NMe2),
6.87 (1 H, d, J = 8.0 Hz, Harom), 6.97 (1 H, d, J = 7.7 Hz,
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 2515–2518

2518
E. A. Filatova et al.
CLUSTER
Harom), 7.31–7.41 (4 H, m, Harom), 7.58–7.67 (3 H, m, Harom),
8.04 (1 H, d, J = 8.3 Hz, Harom). 13C NMR (62.9 MHz,
CDCl3): δ = 44.3, 44.5, 89.6, 93.1, 111.9, 112.9, 113.3,
119.9, 120.6, 124.7, 126.8, 128.1, 128.7, 131.1, 131.8,
138.1, 151.5, 151.9. IR: 2201 (C≡C) cm–1. MS: m/z (%) =
314 (100) [M]+, 299 (19), 283 (44), 268 (76), 226 (21), 134
(13). Anal. Calcd for C22H22N2: C, 84.04; H, 7.05; N, 8.91.
Found: C, 83.92; H, 7.21; N, 9.10.
H
arom), 7.51 (1 H, d, J = 8.0 Hz, Harom), 7.88 (1 H, dd, J = 8.2,
1.1 Hz, Harom). 13C NMR (62.9 MHz, CDCl3): δ = 0.7, 44.3
44.4, 97.5, 105.3, 111.6, 112.7, 113.2, 119.6, 119.8, 126.8,
131.5, 138.2, 151.4, 152.0. IR: 2144 (C≡C) cm–1. Anal.
Calcd for C19H26N2Si: C, 73.49; H, 8.44; N, 9.02. Found: C,
73.41; H, 8.27; N, 9.19.
4-Ethynyl-1,8-bis(dimethylamino)naphthalene (8d)
Dark yellow oil. 1H NMR (250 MHz, CDCl3): δ = 2.76 (6 H,
s, NMe2), 2.81 (6 H, s, NMe2), 3.36 (1 H, s, ≡CH), 6.79 (1 H,
d, J = 7.9 Hz, Harom), 6.92 (1 H, dm, J = 7.6 Hz, Harom), 7.37
(1 H, dd, J = 7.6, 8.2 Hz, Harom), 7.54 (1 H, d, J = 8.0 Hz,
Harom), 7.90 (1 H, dd, J = 8.2, 1.0 Hz, Harom). 13C NMR (62.9
MHz, CDCl3):  = 44.3, 44.4, 80.5, 83.8, 105.3, 111.6,
113.3, 119.6, 121.9, 126.9, 131.9, 138.3, 151.5, 152.2. IR:
2085 (C≡C), 3290 (≡CH) cm–1. Anal. Calcd for C16H18N2: C,
80.63; H, 7.61; N, 11.75. Found: C, 80.74; H, 7.47; N, 11.59.
For general procedures and other experimental and
analytical details see the Supporting Information.
(14) (a) Pozharskii, A. F.; Ozeryanskii, V. A. Russ. Chem. Bull.
1998, 47, 66. (b) Farrer, N. J.; McDonald, R.; McIndoe, J. S.
Dalton Trans. 2006, 4570. (c) Farrer, N. J.; Vikse, K. L.;
McDonald, R.; McIndoe, J. S. Eur. J. Inorg. Chem. 2012,
733.
1,8-Bis(dimethylamino)-4-(p-tolylethynyl)naphthalene
(8b)
Yellow solid; mp 94–96 °C (from EtOH). 1H NMR (250
MHz, CDCl3): δ = 2.36 (3 H, s, CMe), 2.78 (6 H, s, NMe2),
2.82 (6 H, s, NMe2), 6.84 (1 H, d, J = 8.0 Hz, Harom), 6.95 (1
H, dd, J = 7.7, 1.1 Hz, Harom), 7.16 (2 H, d, J = 8.1 Hz, Harom),
7.39 (1 H, dd, J = 7.7, 8.1 Hz, Harom), 7.49 (2 H, dm, J = 8.1
Hz, Harom), 7.57 (1 H, d, J = 8.0 Hz, Harom), 8.00 (1 H, dd, J
= 8.1, 1.1 Hz, Harom). 13C NMR (62.9 MHz, CDCl3): δ = 21.9,
44.4, 44.5, 88.8, 93.2, 112.0, 113.3, 119.8, 119.9, 120.0,
121.6, 126.7, 129.5, 130.9, 131.7, 138.0, 138.1, 151.4,
151.7. IR: 2140 (C≡C) cm–1. MS: m/z (%) = 328 (100) [M]+,
313 (19), 297 (44), 284 (38), 268 (14), 239 (18), 149 (21),
140 (30), 134 (14), 127 (13). Anal. Calcd for C23H24N2: C,
84.11; H, 7.37; N, 8.53. Found: C, 84.28; H, 7.15; N, 8.46.
1,8-Bis(dimethylamino)-4-(trimethylsilylethynyl)-
naphthalene (8c)
(15) Staab, H. A.; Kirsch, A.; Barth, T.; Krieger, C.; Neugebauer,
F. A. Eur. J. Org. Chem. 2000, 1617.
(16) Boiko, L. Z.; Sorokin, V. I.; Filatova, E. A.; Starikova, Z. A.;
Ozeryanskii, V. A.; Pozharskii, A. F. J. Mol. Struct. 2011,
1005, 12.
Yellow solid; mp 108–109 °C (from MeOH). 1H NMR (250
MHz, CDCl3): δ = 0.27 (9 H, s, SiMe3), 2.74 (6 H, s, NMe2),
2.79 (6 H, s, NMe2), 6.77 (1 H, d, J = 8.0 Hz, Harom), 6.91 (1
H, dd, J = 7.6, 1.1 Hz, Harom), 7.36 (1 H, dd, J = 7.6, 8.2 Hz,
Synlett 2013, 24, 2515–2518
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